Lifting devices that are supported either on the ground surrounding the building whose roof is to be lifted, or that are supported on a floor or story of the building are already known. For example, reference may be made to documents WO-A-94 11596 and FR-A-2 540 543 which describe lifting devices using jacks supported on a floor of the building whose roof is to be raised. Reference may also be made to document U.S. Pat. No. 4,980,999 which describes a lifting device supported on the surrounding ground, and constituted either by lifting towers incorporating winch systems, or else by jacks mounted on a support itself standing on the ground.
Those known devices are not organized to be capable of being fixed to the surface of a wall, and in addition their structure is extremely bulky, thus giving rise to high manufacturing cost.
Document FR-A-2 720 430 in the name of the Applicant and published on Dec. 1, 1995, describes a lifting device of the above type, and comprising:
support means suitable for being fixed to a substantially vertical surface of a wall, in particular an outside surface thereof; PA1 a cursor suitable for being placed substantially vertically above the support means and for co-operating with an element of the framework resting thereon; PA1 guide means for guiding the cursor in translation relative to the support means, in a direction that is capable of being oriented substantially vertically; and PA1 in an application to lifting a roof, and in an embodiment in which the support means are constituted by three distinct wall plates that are fixed independently of one another to the wall, comprising a low plate serving as a support for a jack constituting the controlled thrust means, and a high plate and an intermediate plate co-operating with stanchions carrying the cursor for the purpose of constituting guide means therefor.
That embodiment of a device for lifting a roof suffers from the drawback of being complex, expensive to manufacture, lengthy and fiddly for fixing to and adjusting on the surface of a wall, lengthy to dismantle after the roof has been lifted to the desired level and the wall has been built up to the roof lifted in this way, and it is particularly detrimental to the appearance of the wall since it is necessary to drill numerous holes therein for fixing the various plates.